1. Field of the Invention
This invention relates to transmission of sound. In one of its aspects it relates to microphones. In another of its aspects, it relates to lasers. In another of its aspects, it relates to pulsed lasers. In another of its aspects, it relates to the use of modulated, pulsed laser light in the transmission of sound. In yet another aspect, it relates to reduction of electrical interference in the transmission of sound from a microphone. In yet another aspect of the invention, it relates to the elimination of electrical wiring from a microphone to a reception point.
2. Description of the Prior Art
In general, the most common form of microphone can be described as a diaphragm which is exposed to sound waves with the diaphragm coupled in some way with an electrical receiver that translates the vibrations of the diaphragm into electrical signals that can be transmitted, recorded or amplified. From the earliest history of electrical sound reproduction emphasis has been given to providing microphones that are progressively less cumbersome and at the same time are capable of reducing distortion of the sound passed through them. The use of electrical wiring to connect the body of the microphone to an electrical receiver and the attachment of electrical wiring directly to the diaphragm contribute to electrical and mechanical interference with the quality of the transmitted sound.
To overcome these problems, the conversion of sound waves into modulated light has been considered as a means to efficiently bridge the conversion of sound into electrical signals. The prior art, therefore, discloses the use of laser and other light beams in the conversion of sound waves into electrical signals.
U.S. Pat. Nos. 1,709,792; 3,470,329 and 3,622,791 all set out microphones that use light to convert sound waves to electrical signals based on the principles of an interferometer.
U.S. Pat. No. 4,412,105 discloses a system in which a microphone has a cylindrical outer housing with a plurality of circumferentially spaced openings for the entry of sound waves and a cylindrical inner housing positioned concentrically inside the outer housing so that laser light projected into the space between the housings is modulated by sound waves entering the outer housing and the modulated laser light is received by a plurality of analogous photo detectors which produce electrical signals corresponding to the sound waves entering the outer housing by measuring the intensity of the fluctuating (modulated) laser stream which can be reflected from a vibrating diaphragm. This patent specifically seeks the elimination of a vibrating diaphragm in the conversion of sound waves to electrical signals, but some embodiments of the invention show the use of vibrating diaphragms. Detection of the modulation of the laser light is based on direct interpretation of the modulation of the laser light into analog signals.
U.S. Pat. No. 4,479,265 discloses a microphone system in which two aligned beams of laser light, one of which is delayed in relation to the other and is reflected by an object in motion, are used to produce an interference pattern that can be sensed by a light sensor placed in the path of the aligned beams. Detection of the modulation of the laser light, as in the discussion above, is based on direct interpretation of the modulation of the laser light into analog signals.
3. Objects of the Invention.
It is therefore an object of this invention to convert sound waves to modulated, pulsed laser light for the purpose of transmitting the modulated, pulsed laser light to a location at which the modulated, pulsed laser light is converted to digital, electrical signals.
It is another object of this invention to provide apparatus by which sound waves can be converted to modulated, pulsed laser light and the modulated, pulsed laser light can be transmitted to a location at which the modulated, pulsed laser light is converted to digital, electrical signals.
These and other objects and advantages of the present invention will become evident to those skilled in the art by reference to the following description and drawing and the appended claims.